This invention relates to a curing catalyst to be employed for curing an epoxy resin or cationic polymerizable compound, and to a resin composition containing the curing catalyst. This invention also relates to a resin-sealed semiconductor device which is sealed using the resin composition and to a coating material containing the resin composition.
Epoxy resin is generally excellent in electric insulation, mechanical strength, adhesivity, moisture resistance, etc. so that epoxy resin is extensively employed for instance in the fields of painting technology for motor cars, cans, etc., in the fields of electricity for sealing materials, laminate boards, etc., in the fields of civil engineering and architecture, and in the field of adhesives. Conventionally, epoxy resin has been commonly employed in a two-part system wherein an amine compound or a carboxylic acid anhydride is included as a curing agent. However, this two-part system employing such a curing agent is troublesome in its use since two parts are required to be mixed together immediately before use. Further, epoxy resin is required to be stored or transported under a low temperature condition, or the useful life after the manufacture thereof is very limited. Under the circumstances, there have been strong demands for years to develop an epoxy resin composition which is capable of being stored in the form of one-pack and at ordinary temperatures, and a large number of methods have been studied for manufacturing such an epoxy resin composition.
In the case of a thermosetting composition whose curing reaction can be promoted by an acid catalyst or a basic catalyst, the potentialization of these catalysts by means of physical method or chemical method has been conventionally studied with a view to improve the storage stability of the thermosetting composition. For example, as for the physical method, there have been proposed a method wherein an organic phosphine compound for instance is encapsulated using a polymer thereby forming granular microcapsules (Japanese Patent Unexamined Publication H6-73163), or a method wherein the catalysts are allowed to be adsorbed to a porous compound such as zeolite, thereby assuring the storage stability of the thermosetting composition in the form of one-pack. However, these conventional physical methods are accompanied with problems that it is difficult to secure a sufficient potentialization (latency) of these catalysts, that since these catalyst systems are of heterogeneous system, they cannot be employed in a processing method such as impregnation, thus limiting the end-use thereof, and that a curing resin may easily become non-uniform.
On the other hand, as for the chemical method, there has been extensively studied a method to employ so-called a heat-latent catalyst whose activity can be temporarily inhibited and can be reactivated as it is cleaved at the occasion of thermal cure thereof. As for such a heat-latent catalyst, there are known a catalyst whose active proton is blocked by taking advantage of a neutralization reaction of acid-base, or a catalyst whose active proton is blocked by taking advantage of an esterification reaction thereof with alcohols (Japanese Patent Publication S52-770). There are also known, as a heat-latent catalyst which is capable of generating an active benzyl cation through a thermal decomposition of onium salt, a benzyl sulfonium salt type catalyst or a benzyl pyridinium salt type catalyst (Japanese Patent Unexamined Publication S62-192427). As for a heat-latent catalyst which is now commercially available, Lewis acids such as a boron trifluoride-monoethyl amine complex and a boron trifluoride-pyridine complex are known.
However, the catalysts produced by taking advantage of a neutralization reaction of acid-base, or by taking advantage of an esterification reaction thereof with alcohols are hardly capable of providing a heat-latent catalyst having a suitable dissociation temperature and heat stability. On the other hand, the benzyl sulfonium salt type or the benzyl pyridinium salt type catalyst is relatively excellent in storage stability but is not sufficient enough for practical use. Particularly, alicyclic epoxy resins which are highly reactive are poor in storage stability. Further, the aforementioned boron trifluoride-monoethyl amine complex and boron trifluoride-pyridine complex which are commercially available now are generally too high in dissociation temperature.
As mentioned above, when these conventional catalysts are employed together with a curing resin component or an epoxy resin, the curing reaction of the epoxy resin takes place gradually immediately after these catalysts are mixed with the epoxy resin even if the epoxy resin composition is kept at room temperature. Namely, even if such an epoxy resin composition is simply kept stored, the curing reaction of the resin composition continues to proceed though gradually, and ultimately cured. Therefore, the storage period of the epoxy resin composition is restricted to a certain limited period of time, thus requiring the epoxy resin composition to be used up by this limited storage period.
Further, since the curing reaction to be induced by these conventional catalysts takes place through an ionic reaction, an ionic catalyst is caused to be left remained in the cured resin after the curing reaction, whereby greatly deteriorating the electric insulation property of the cured resin.
Meantime, Lewis acids such as BF3, AlCl3, AlRCl2, etc. are known as being useful as a cationic polymerization catalyst for a cationic polymerizable vinyl compound. However, these polymerization catalysts cause the polymerizable compound to proceed the polymerization reaction thereof even at low temperatures such as room temperature, thus making the resultant polymerizable composition very poor in storage stability. Additionally, it becomes difficult to control the polymerization reaction and to obtain a high polymerization degree. In the case of polymerization of a vinyl compound, a polymerization catalyst is generally charged into a monomer after the monomer which has been dissolved in a suitable solvent in advance is cooled down to a predetermined very low temperature. However, since the operation of industrially executing the polymerization reaction at a low temperature region is very troublesome and costly, the method using such polymerization catalysts is not appropriate.
Accordingly, an object of the present invention is to provide a curing catalyst for a resin composition, in particular an epoxy resin composition, which is capable of causing a polymerization reaction to be quickly taken place at a predetermined temperature higher than room temperature thereby curing the resin, and incapable of causing the polymerization reaction to take place at a temperature not higher than room temperature.
Another object of the present invention is to provide a resin composition of excellent workability which is incapable of causing the curing reaction to take place at a temperature not higher than room temperature, thereby ensuring the resin composition to have a high storage stability, and capable of causing a curing reaction to quickly take place at a predetermined temperature higher than room temperature thereby making it possible to obtain a cured product having excellent electric insulation and excellent mechanical strength.
Still another object of the present invention is to provide a resin-sealed semiconductor device having a high thermal shock resistance and a moistureproof reliability, which is sealed using an epoxy resin composition which is excellent in storage stability, fluidity and filling property.
Further object of the present invention is to provide a coating material containing the aforementioned curing catalyst, and exhibiting an excellent storage stability and a high hardness after the curing of the coating material.
Namely, according to the present invention, there is provided a curing catalyst comprising at least one of a cationic curing catalyst component and an organometallic compound component, wherein at least one of these components is capable of reversibly the dissolving and precipitating through heating and cooling.
Further, according to the present invention, there is provided a curing catalyst comprising at least one kind of compound selected from the group consisting of compounds represented by the following general formulas (III-1xe2x80x2) and (III-2): 
wherein R1, R2 and R3 may be the same or different and are individually hydrogen atom, a substituted or unsubstituted hydrocarbon group having 1 to 30 carbon atoms, an aromatic group having a substituted or unsubstituted hydrocarbon group, or a heteroaromatic group having a substituted or unsubstituted hydrocarbon group, with a proviso that at least one of R1, R2 and R3 is a substituted or unsubstituted hydrocarbon group having 10 or more carbon atoms, an aromatic group having a substituted or unsubstituted hydrocarbon group having 10 or more carbon atoms, or a heteroaromatic group having a substituted or unsubstituted hydrocarbon group having 10 or more carbon atoms; and 
wherein R32, R33, R34 and R35 may be the same or different and are individually hydrogen atom or a substituted or unsubstituted hydrocarbon group having 1 to 30 carbon atoms with a proviso that at least two of R32, R33, R34 and R35 has not less than 10 carbon atoms.
Further, according to the present invention, there is provided a curing catalyst comprising at least one kind of compound selected from the group consisting of compounds represented by the following general formulas (III-1) to (III-2): 
wherein R31s may be the same or different and are individually hydrogen atom or substituted or unsubstituted hydrocarbon groups having 1 to 30 carbon atoms with a proviso that at least one of R31s has not less than 10 carbon atoms; h, i and j are integers satisfying a condition of h+i+j=3; and m is an integer of 1 to 5; 
wherein R32, R33, R34 and R35 may be the same or different and are individually hydrogen atom or substituted or unsubstituted hydrocarbon groups having 1 to 30 carbon atoms with a proviso that at least two of R32, R33, R34 and R35 has not less than 10 carbon atoms.
Furthermore, according to the present invention, there is provided a resin composition comprising the aforementioned curing catalyst and a cationic polymerizable resin component.
Further, according to the present invention, there is provided a resin-sealed semiconductor device comprising: a semiconductor element; and a resin layer sealing the semiconductor element; wherein the resin layer is constituted by a cured body of the aforementioned resin composition.